The present invention relates to a duplex copying method of making duplex copies from one side originals, using an electrophotographic duplex copying machine provided with an auto document feeder.
Conventional electrophotographic duplex copying machines are provided with an auto document feeder (hereinafter referred to as ADF) or a recycling auto document feeder (hereinafter referred to as RADF), which is mounted on a contact glass, a duplex copy tray and a transfer sheet inverting apparatus, and are capable of performing (i) a one-side original--duplex copy mode of making a duplex copy from two originals, each original bearing images on one side thereof only (hereinafter referred to one-side original), or (ii) a duplex original--duplex copy mode of making a duplex copy from a duplex original which bears images on both sides.
The basic operation of the one-side original--duplex copy mode comprises the steps of successively feeding one-side originals, which are stacked in the order of the pages with the respective image side down on an original input tray, onto a contact glass in the order of the pages by an ADF or by a RADF, transporting a transfer sheet to an image transfer station, thereby making a copy which bears the image copied from a first, odd-numbered original at an image transfer station, temporarily holding the corresponding odd-numbered image bearing transfer sheet in a duplex copy tray, feeding again the transfer sheet from the duplex copy tray to the image transfer section, transferring the image corresponding to the image of the next even-numbered original to the back side of the transfer sheet to make a duplex copy, and discharging the duplex copy with the odd-numbered image side down onto a copy sheet output tray, whereby duplex copies are stacked on the copy sheet output tray in the order of the pages, for instance, with the first page down, the second page up, the third page down, and the fourth page up, so forth.
In the above one-side original--duplex copy mode, when the total number of one-side originals is an odd number, it is always a problem how to perform the copying operation of the last original. More specifically, when the total number is an odd number, it is necessary to discharge a one-side copy sheet which bears only at the first side the image corresponding to the image of the last original, with the image side down, onto the copy sheet output tray, in the order of the pages.
For instance, in a conventional electrophotographic copying machine with an ADF apparatus, the copying operation is performed in the same way, regardless of whether the total number of one side originals is an even number or an odd number. For instance, when the total number is an odd number, the transfer sheet which bears the image corresponding to the original image (hereinafter referred to as the one-side copy sheet) is temporarily held in a duplex copy sheet tray and upon detection of a signal indicating that there remains no more original in an original input tray, the one-side copy sheet is fed from the duplex copy sheet tray again to the image transfer station, then transferred to the image fixing station, without image transfer and image fixing, and is finally discharged to the copy sheet output tray. In other words, in the above, the copying process is performed as if there was a blank original after the last odd-numbered original, so that the last copy sheet is uselessly caused to pass through the image transfer station and the image fixing station. The last copy sheet transportation process, which should be omitted if possible, will obviously increase the opportunity of copy sheet jamming.
Furthermore, for working out this problem, there is proposed in Japanese Laid-Open Patent Application No. 59-74574 an electrophotographic copying machine provided with a RADF. In this electrophotographic copying machine, prior to copying operation, it is determined whether or not the total number of one-side originals is an odd number by setting the originals in the RADF and counting the number by the RADF. When the total number is an odd number, the unnecessary transportation of the last one-side copy sheet, for instance, through the image transfer station and the image fixing station, is skipped. For this process, however, an expensive RADF apparatus is necessary and it is always necessary to count the total number of one-side originals to be copied prior to the copying thereof.